1. Field of the Invention
This invention relates to a vehicle seat having a head restraint apparatus.
2. Description of the Related Art
Proposed is a movable head restraint apparatus in which a head rest can be moved forward to restrain the head of an occupant in case of a rear-end collision of a vehicle or the like. A head restraint apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 11-268566 (patent document 1), for example, comprises a bracket for supporting stays of a head rest and a pressure receiving plate provided on the lower part of the bracket. The bracket rocks back and forth around a shaft that is situated between the head rest and the pressure receiving plate. In the head restraint apparatus of this type, the head rest moves forward if the occupant's body is pressed against a seat back by a collision so that the pressure receiving plate is pushed rearward.
In the head restraint apparatus described in the patent document 1, the amount of forward movement of the head rest is smaller than the amount of movement of the pressure receiving plate. Therefore, the apparatus cannot easily restrain the occupant's head early, so that it can produce only a small injury reduction effect. If the center of rocking motion is lowered, the operating speed of the head rest is increased, so that the occupant's head can be restrained early. In this case, however, the stays of the head rest deeply bend rearward by the load from the occupant's head, so that the injury reduction effect is inevitably lowered. If the stiffness of the stays is enhanced to lessen the deflection of the stays, there arises a problem that the weight of the stays increases.
In a head restraint apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 2001-58533 (patent document 2), a pressure receiving plate is located in the upper part of a seat back. By doing this, the ratio (link ratio) between the distance from the head rest to the center of its rocking motion and the distance from the center of rocking motion of the head rest to the pressure receiving plate is increased.
The head rest described in the patent document 1 is configured so that the head rest and the pressure receiving plate move like a seesaw in opposite directions around an axis between them. Thus, the components of the apparatus tend to increase in size and weight. Further, operation for layout in the seat back is troublesome. In the case of a power seat, moreover, the pressure receiving plate and other moving parts must be arranged lest they interfere with a motor or any other mechanical component of the seat. Thus, the efficiency of layout in the seat back is poor.
Although the pressure receiving plate is located in the upper part of the seat back in the head restraint apparatus described in the patent document 2, it cannot satisfactorily ensure early restraint of the occupant's head. In order to prevent the pressure receiving plate on the upper part of the seat back from causing a foreign body sensation, the pressure receiving plate must be receded as deep behind the seat back as possible in its thickness direction. In this case, there is a problem that the time for the start of operation is delayed.
In the head restraint apparatus described in the patent document 2, the pressure receiving plate is provided in the upper part of the seat back so that it can be pressed by the occupant's back. According to this configuration, compared with a configuration in which the pressure receiving plate is located in the lower part of the seat back, the pressure receiving plate is subjected to a lighter load. Since a seat back frame itself bends rearward and for any other reasons, moreover, the start of operation is inevitably delayed further.